The present invention relates to dynamoelectric machines and particularly to armature windings for large turbine generators.
A conventional turbine-driven generator comprises a stationary core or armature and a cooperating rotatable field element or rotor. The armature is formed of laminations of magnetic material and is provided with an elongated cylindrical opening or bore bounded by a plurality of angularly spaced winding slots in which an armature winding is accommodated. The rotor is journalled for rotation within the armature bore and carries a plurality of pole pieces arrayed about its periphery. Turbine generators capable of generating electrical power in the high MVA range are massive in size, for example the rotors along may weigh 300 tons or more and be in excess of 25 feet in diameter.
In generators of this size, the armature windings necessarily have a considerable conductor cross section typically made up of a plurality of individually insulated aluminum or copper strips or strands bound together in ground insulation jacket. Armature windings are typically of two basic types. In a bar coil armature winding, each winding coil comprises two essentially straight conductors segments or "bars" which are laid in different armature core slots and the appropriate end turn connections or joints therebetween are subsequently made by appropriate means such as welding, brazing or separate electrical connector elements. This winding approach is advantageous in the case of multi-layer armature windings where two or more bars of different coils must be laid in each of the winding slots in stacked relation. This is so since the two bars of each coil typically occupy different radial positions in their respective winding slots. By effecting the appropriate end turn connections after all the bars have been positioned in the winding slots, there is no need to temporarily remove one bar from its uppe slot position to lay another bar in a lower slot position of the same winding slot. An additional advantage of the bar coil winding approach is that repair or replacement of damaged coils is facilitated. Fewer coils need to be removed to access damaged coils and less disassembly of the generator is required to effect repair or replacement. The major disadvantage of the bar coil winding approach is that the winding process is very time consuming and expensive.
As a more economical approach, turbine generator manufacturers have resorted to utilizing form coil armature windings, wherein the insulated winding conductor strands are machine wound into so-called "diamond" coils comprising two straight coil sides and integrally interconnecting end turn sections. Each diamond coil is then provided with a ground insulation jacket that binds the conductor strands together to create a rather rigid structure which in the case of large turbine generators can weigh in excess of one hundred pounds. These diamond coils are then used to wind the armature by progressively laying their straight coil sides in the armature winding slots. Since for a multi-layer winding, the two sides of each coil typically occupy radially different positions in their respective slots, it becomes necessary toward the end of the winding processes to perform the step known as "fanning" or "raising the jump". This step involves lifting one side of previously placed diamond coils temporarily out of their slots in order to lay the sides of later-placed diamond coils therebeneath in lower slot positions. Since the other sides of the lifted or fanned coils are lodged in lower positions in their respective slots, the coils must be forcibly deformed to elevate their one sides out of the slots. This deformation, sometimes facilitated by heating the coils, if not carefully performed, can damage the coil insulation. While diamond coil wound armature windings are more economical to wind in the first instance, they are not so when it becomes necessary to repair or replace damaged coils. As noted above in connection with bar coil armature windings, a significant number of diamond coils must be removed and considerable generator disassembly is required to gain access to damaged coils. Typically, to access damaged coils, the turbine rotor has to be removed using heavy rigging equipment. This is particularly so if the armature has to be completely rewound, which for large turbine generators must be done in the field. Some generating sites are not equipped with adequate rigging equipment to pull the turbine rotor and may be in remote locations where such heavy equipment can not be readily brought in.
It is accordingly an object of the present invention to provide an improved armature winding for large turbine generators.
A further object is to provide an armature winding of the above-character which is more convenient to wind.
Another object is to provide an armature winding of the above-character which can be applied to turbine generators in the field in an expeditious and economical manner.
An additional object of the present invention is to provide an improved method for winding the armature of a large turbine generator.
Yet another object is to provide an improved method for rewinding the armature of a turbine generator in the field.
Other objects of the invention will in part be obvious and in part appear hereinafter.